Understanding Power Supply Requirements for Your Effects Pedals

Published Thursday, November 23, 2017 by DrKev

People often ask me about powering their effects pedals. Pedals manufacturers’ specifications can be confusing and people are naturally afraid of damaging their pedals by using the wrong device. But with a little care we have nothing to fear. Let’s clear up the confusion and answer the common questions.

Power adapters are known by many names: AC adaptor, AC/DC adaptor, AC/DC converter, or, a PSU or power supply unit. Their electrical output is described by four things – the voltage they provide, the type of voltage (i.e. AC or DC), the maximum current the adaptor can supply, and when the output is a DC voltage the polarity of the voltage at the output plug. While this might sound complicated, we don’t need to worry because the vast majority of guitar effects pedals on the market today require 9 V DC supplied through a centre negative plug (and those few that don’t usually make it very clear). The amount of current required depends on the individual pedals but that rarely causes us trouble either.

“Why do some people call it an ‘AC power adaptor’? Don’t pedals use DC? How do I know what to use?”

They are sometimes called AC power adaptors because they take an AC voltage (e.g. from the outlet from the wall that powers our TV or guitar amplifier) and ‘adapt’ it to produce something else (in our case a smaller DC voltage). It will be clearly marked on the device what the output voltage will be. AC voltage is denoted by “AC V”, or “V AC”, or a squiggle, e.g. 9 V ~ . Most guitar effects pedals don’t use AC power.

DC voltages are labelled V DC, or with DC symbol of a broken line under a solid line, like this: 9 V ⎓​. Polarity (which way the DC voltage is presented to the pedal) is denoted by a little symbol that looks like two connected balls that tells us which part of the plug is + (positive) or – (negative), like this…

If we use an adaptor that supplies AC voltage into our pedal instead of DC, or DC of the wrong polarity, or too high a voltage, the pedal won’t work and there is a chance we could destroy the pedal. If the DC voltage is too low the sound quality will suffer or the pedal may not switch on.

No, it won’t damage your pedal all. Do not think of power adaptors pushing current into our effects pedals. Instead the power adaptor simply presents a voltage to the pedal and the pedal draws the current it needs from the adaptor. The pedal is in control!

In this example, the addition of “max” to “300 mA max” is particularly confusing. But this is simply the pedal manufacturer’s recommendation for the adaptor’s maximum rated current. It does not mean you should avoid using an adaptor capable of delivering more than 300 mA. An adaptor with a lower current rating than required may not be able to supply sufficient power for the pedal to operate as intended. But, as we now know, a pedal will only draw as much current as it needs, so any adaptor with a higher current rating than recommended is perfectly safe.

The advantage of using power adaptors rated for higher currents than a pedal needs is that we can power a number of different pedals at the same time (e.g. by using of daisy chain adaptor). And the more current an adaptor can deliver, the more pedals you can power! How many? Well, that depends on the pedals and the adaptor…

“I have three digital pedals that need 100 mA, my tuner requires 50 mA, and I have a three old analog distortion pedals. What adaptor rating do I need?”

Here, we just do the math and add up the current draws. The analog pedals will usually draw less than 20 mA each, maybe less than 10 mA, but lets use 20 mA to gives us a margin of error. So…

(3 x 100 mA) + 50 mA + (3 x 20 mA) = (300 + 50 + 60) mA = 410 mA

An adaptor rated up to 400 mA will be have reached its rated operating limit powering all those pedals. Depending on the design of the adaptor it may switch off, overheat, or fail to maintain the voltage we need. In this example where we need approx 400 mA of current, I would choose an adaptor rated to at least 800 mA. Going even higher, say 1200 mA or even 2000 mA, is perfectly safe for the pedals and gives us freedom to add many additional pedals in the future. 1200 mA will allow us to power 10 or 12 digital effects pedals, or more than 50 analog pedals.

If the current draw of a particular effect pedal is not listed by the manufacturer, you can look it up on Sintkfoot.se, which has a fantastic web resource called The Power List.

“When I turn off an effect, does it still take power from the adaptor?”

In general, yes. Even when the effect is switched off, most pedals are still operating, they are just not affecting your signal. Some modern pedals have been designed with reduced or almost zero power consumption in bypass mode but they are a minority of pedals out there. If you are not sure what your pedal does, assume that once it is connected it’s drawing its required current at all times.

“Can I use a cheap adaptor I bought at a local hardware store?”

Maybe but it’s best to avoid them. Adaptors designed for use with our effects pedals are usually ‘voltage regulated’, meaning the output voltage will stay constant up to the adaptors maximum current. Cheaper general purpose adaptors are often unregulated. This means the voltage will drop as the current draw increases. The voltage could be too high at low current draws. The volatge cheap adaptors deliver is often ‘unfiltered’ which can cause unpleasant noise through our guitar pedals and amplifier.

“My tuner pedal manual says to use either a 9 V battery, or an AC adapter supplying 9 VDC at 600 mA. Why would a floor tuner need 600 mA adaptor if it could also run on battery?”

Indeed, no single effect pedal of any description draws anything close to 600 mA. If it did, you’d be changing the battery every ten minutes! (Though large multieffects units might draw even more than that).

Let’s say we have a modern digital pedal tuner that requires about 50 mA. But if we used an unregulated 100 mA max adaptor, the voltage could still drop lower than required if we powered another pedal or two at the same time. In this example, the manufacturer is playing it safe by specifying an adaptor that even if unregulated won’t drop below the minimum voltage for the pedal, unless many other pedals are also connected.

“My pedal does not have an adaptor input jack, just a battery compartment. Can I safely connect an AC power adaptor to the pedal’s battery terminals?”

Yes, pedals don’t care where the voltage comes from provided it’s the right voltage. In fact you can buy battery clip adaptors specifically designed for this purpose.

“Which power adaptor should I buy?”

I recommend choosing an adaptor designed for use with effects pedals with highest current output with that you can afford that suits your pedal board’s size and portability needs. I’ve had many years of trouble-free operation with 1Spot adaptors. They are small, powerful, have a long cable and I can power multiple pedals with their daisy chain adaptors. They are equally happy supplying 9 V to one simple pedal or to 20, right up the its current limit of 1700 mA. But there are many other great options on the market in a variety of sizes and shapes, power ratings, and some can even deliver multiple voltages and polarities.

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